Comparative study of in-cylinder tumble flows in an internal combustion engine using different piston shapes—an insight using particle image velocimetry

This paper deals with the experimental investigations of the in-cylinder tumble flows in a single-cylinder engine with five different piston crown shapes at an engine speed of 1,000 rev/min., during suction and compression strokes under motoring conditions using particle image velocimetry. Two-dimensional in-cylinder tumble flow measurements and analysis are carried out in combustion space on a vertical plane passing through cylinder axis. Ensemble average velocity vectors are used to analyze the tumble flow structure. Tumble ratio and average turbulent kinetic energy are evaluated and used to characterize the tumble flows. From results, it is found that at end of compression, pentroof-offset-bowl piston shows about 41 and 103% improvement in tumble ratio and average turbulent kinetic energy respectively, compared to that of flat piston. The present study will be useful in understanding effect of piston crown shapes on nature of the in-cylinder fluid tumble flows under real engine conditions.